Wear measurement and durability evaluation method for rock cutting tools

Abstract

The present invention relates to a method for measuring and evaluating the wear and durability of rock cutting tools using rock test pieces, and using this method as an accelerated life test, specifically a trouble-free accelerated test method that increases at least one of the cutting load and the cutting speed and uses reliable excavation volume instead of the concept of reliable time to define the reliable life.

Description

[0001] This application claims the priority of Korean Patent Application No. 10-2020-0143971 (filed on October 31, 2020), and all the contents in the specification and drawings of that application are incorporated into the specification of this application. Technical Field

[0002] The present invention relates to a wear measurement and durability evaluation method for rock cutting tools. Specifically, the present invention relates to a method for performing a pin-on-disk test specified by ASTM, (i) a method for forming an Archimedean spiral trajectory at a certain speed during the process of the cutting tool moving inward and outward alternately and repeatedly on a rock test piece, (ii) a method for implementing the wear measurement and durability evaluation method of (i) above on a hollow test piece, (iii) a method for designing and providing a trouble-free accelerated test by using the method of (ii) above as an accelerated life test by increasing the cutting load and / or cutting speed and replacing the reliable time concept with the concept of reliable excavation volume to define the reliable life. Background Art

[0003] Generally, the durability of rock / resource cutting tools installed on roadheaders, continuous miners, and TBMs is directly related to work efficiency.

[0004] However, there is no standard test method or recognized test method that can quantitatively evaluate the durability of rock cutting tools. ASTM (American Society for Testing and Materials) has published the pin-on-disc test and the pin-on-drum test, which are used to test metal-to-metal wear and are therefore not suitable for direct application to rock specimens with large cutting volumes.

[0005] like Figure 1 As shown in the figure, the pin-on-disc test is a process in which a pin moves linearly in a radial direction while a disk-shaped test piece rotates about a vertical axis, causing wear. In order to perform the pin-on-disc test, the cutting tool needs to form an Archimedean spiral trajectory on the test piece at a constant speed (constant speed).

[0006] However, ASTM did not specify the motion equations and control methods for the pin and the test piece. It only explained the basic principles and diagrams of the wear test method for metal test pieces. It did not specifically record the specific control methods, motion equations, and data extraction methods for test pieces that are severely worn, such as rocks and concrete. Summary of the invention

[0007] Technical issues

[0008] The present invention aims to solve these problems and has the object of providing a method for measuring wear and evaluating durability of a rock cutting tool: the pin-to-disc test specified in ASTM can be applied to a rock cutting tool and a rock test piece, the cutting tool moves inward and outward alternately and repeatedly and cuts the rock test piece during the process of moving along different Archimedean screws when moving inward and outward, the end point of the inward movement becomes the starting point of the outward movement, and the end point of the outward movement becomes the starting point of the inward movement, and the rotation direction of the rock test piece is the same when moving outward and inward.

[0009] Another object of the present invention is to provide a wear measurement and durability evaluation method for rock cutting tools that can be applied to hollow rock specimens so as to solve the problems that occur when the above evaluation method is used for solid type rock specimens.

[0010] Another object of the present invention is to use hollow rock specimens for testing by increasing the cutting load and / or cutting speed as an accelerated life test, thereby replacing the concept of reliable time in reliability engineering and using the concept of reliable excavation volume to define reliable life and provide a trouble-free accelerated testing method.

[0011] Technical Solution

[0012] In order to solve the problem described in [Background Technology], the present applicant discloses a cutting tool such as Figure 2 A measurement method using the governing equation for the Archimedean spiral trajectory formed when a solid rock specimen (a rock specimen with a full core) moves at a constant speed has been developed.

[0013] In the above-mentioned measuring method, the rock specimen 1 is rotated with the rotation axis 112 as the reference, and the cutting tool 10 cuts the rock specimen 1 during the process of linearly moving from the center to the outer contour of the upper surface 3 of the rock specimen 1 or from the outer contour to the center, thereby forming a spiral trajectory on the upper surface 3.

[0014] Specifically, the rotational force of the driving motor 110 is transmitted to the specimen fixing part 130 through the rotating shaft 112, so that the rock specimen 1 rotates. The cutting tool 10 is linearly moved from the center to the outer contour of the rock specimen 1 (in the direction of the arrow) when being pressurized or displaced by a load unit (not shown), or linearly moved from the outer contour to the center of the rock specimen 1, or repeatedly reciprocated between the center and the outer contour. The cutting tool 10 can achieve linear movement through a linear moving unit (not shown).

[0015] According to the measuring method, the radius (R) of the outermost part of the spiral, the time (T) required for the cutting tool 10 to move once along the spiral trajectory, and the number of spirals (N) are received from the user, and the spiral trajectory, the distance from the center to the cutting tool (r), the rotation angle (θ) of the rock specimen 1, the distance (L) moved by the cutting tool 10 along the spiral trajectory, and the speed (V) of the cutting tool 10 along the spiral trajectory are calculated using the following formula: L )wait. Figure 3 The definitions of the radius (r) and the rotation angle (θ) of the spiral are shown.

[0016] [Formula 1]

[0017]

[0018] [Formula 2]

[0019]

[0020] In the above formula, t: time, R: radius of the outermost part of the spiral,

[0021] N: number of spirals (e.g. Figure 3 N = 5), θ(t): the rotation angle of the rock specimen,

[0022] T: The time required for the cutting tool to move from the center to the outer contour or from the outer contour to the center along the spiral trajectory.

[0023] Furthermore, when the cutting tool 10 is linearly moved in the radial direction and the rock specimen is rotated using the above calculation results, the cutting tool 10 forms an Archimedean spiral trajectory at a certain speed on the upper surface 3. At this time, the intervals between the spiral trajectories are constant. Figure 4 The Archimedean spiral trajectory formed by the cutting tool in the case of an outward spiral is shown.

[0024] However, since equations 1 and 2 include trigonometric functions regarding time (t), it is absolutely impossible to calculate the radial speed and rotational speed that satisfy the constant speed simply by inverse calculation (solving the equation) (that is, it is impossible to calculate the exact solution to the differential equation).

[0025] In addition, in the fields of atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM), in order to improve the scanning quality, a method of moving the Archimedean screw at a constant linear velocity (CLV) has been studied as follows.

[0026] D Ziegler et al., “Ideal Scan Paths for High-Speed ​​Atomic Force Microscopy”, IEEE / ASME Transactions on Mechatronics, 22(1), 381-391, 2016. (DOI: 10.1109 / TMECH.2016.2615327)

[0027] IA Mahmood and SO Reza Moheimani, Spiral Scanning Atomic Force Microscopy: Constant Linear Velocity Method, Proceedings of the 10th IEEE International Conference on Nanotechnology in Korea 2010 Nanosymposium, KINTEX, Korea, 2010 (DOI: 10.1109 / NANO.2010.5698063)

[0028] X Sang et al., “Dynamic scan control in STEM: spiral scanning”, Advanced Structural and Chemical Imaging, 2(6), 2017. (DOI: 10.1186 / s40679-016-0020-3

[0029] According to the research results, in the path moving from the inside to the outside of the circle (outward path), the spiral radius (r) and the rotation angle (θ) can be expressed as the following equations 3 and 4.

[0030] [Formula 3]

[0031] r(t)=R·f(t * )

[0032] [Formula 4]

[0033] θ(t)=2πN·f(t * )

[0034] In the above formula, t * :t / T

[0035] f(t*): When the cutting tool moves linearly from the center to the outer contour of the rock specimen, f(t * ) is an arbitrary function satisfying f(0) = 0, f(1) = 1. When the cutting tool moves linearly from the outer edge to the center of the rock specimen, f(t*) is an arbitrary function satisfying f(0) = 1, f(1) = 0.

[0036] See the above research (paper), in the case of outward spiral, open Inward spiral

[0037] Will Substituting into equations 3 and 4 and differentiating t, we can obtain equations 5 and 6.

[0038] [Formula 5]

[0039]

[0040] [Formula 6]

[0041]

[0042] The linear movement speed of the cutting tool in the case of outward spiral is shown in Formula 5. However, in the case of t=0, for example, when 0≤t≤1, the linear movement speed is too large, so a certain linear movement speed may be input to the device in actual testing.

[0043] In addition, Equation 6 shows the rotation speed of the rock specimen in the case of an outward spiral. However, at the beginning of the measurement near t = 0 (for example, when 0 ≤ t ≤ 0.1 seconds), the rotation speed temporarily increases excessively and then converges to a certain speed. Therefore, after the actual measurement, this part needs to be considered when processing the result data. This part is an error in the approximate solution, which occurs in a small amount within a time period of 0.1 seconds, so it is an error of a negligible degree.

[0044] In addition, in the case of an inward spiral Substituting into equations 3 and 4 and differentiating with respect to t, we can obtain equations 7 and 8. Figure 5 The figure shows the Archimedean spiral trajectory formed by the cutting tool in the case of an inward spiral.

[0045] [Formula 7]

[0046]

[0047] [Formula 8]

[0048]

[0049] Formula 7 shows the linear movement speed of the cutting tool in the case of an inward spiral. However, in the case of t=T, for example, when T=100 seconds (sec), when 99.9 seconds ≤ t ≤ 100 seconds, the linear movement speed increases excessively and converges to a certain speed, so the user needs to consider this when processing data. However, this is also an error that occurs in a very short time and is negligible to the user.

[0050] As described above, the applicant disclosed a control equation for a cutting tool to move at a certain speed while forming an Archimedean spiral trajectory on a solid rock specimen, and developed a measurement and evaluation method using the control equation. Compared with the existing linear cutting test (for example, Korean KR 701979B1, etc.), the method has the advantages of being simple and saving test time.

[0051] In addition, the solid rock specimen has the problem that the cutting depth of the cutting tool cannot be adjusted at the center. Figure 6 As shown, the cutting depth (d 1 , d 2 The cutting depth can be adjusted by inserting the cutting tool into the outer contour of the test piece. However, it is difficult to adjust the cutting depth of the cutting tool in the center of the test piece. Therefore, the test can only be performed with an inward spiral and it is difficult to perform the test with an outward spiral. Figure 7 As shown, there is also a problem that when cutting is performed to a certain depth or more, the tool holder interferes (collides) with the center of the test piece.

[0052] In order to solve these problems, a new control equation for the cutting tool to form an Archimedean spiral trajectory on a hollow test piece (a test piece with a hollow center) at a certain speed was proposed, and a wear measurement and durability evaluation method using this control equation was developed. In addition, a method was developed to use this method as an accelerated life test by increasing the cutting load and / or cutting speed, and to calculate the trouble-free accelerated excavation volume using the reliable excavation volume instead of the reliable life.

[0053] Technical Effects

[0054] The present invention has the following effects.

[0055] First, a wear measurement and durability evaluation method for a rock cutting tool is provided, in which the pin-on-disc test specified by ASTM can be applied to the rock cutting tool and the rock test piece, the cutting tool moves inward and outward alternately and repeatedly, and the cutting tool cuts the rock test piece in the process of moving along different Archimedean spirals when moving inward and outward, the end point of the inward movement becomes the starting point of the outward movement, and the end point of the outward movement becomes the starting point of the inward movement, and the rotation direction of the rock test piece is the same when moving outward and inward.

[0056] Second, a new control equation is provided to enable the above method to be applied to blank test pieces.

[0057] Third, the test of hollow test pieces is conducted as an accelerated life test by increasing the cutting load and / or cutting speed, and the reliable life is defined by the reliable excavation volume instead of the reliable time concept, and a trouble-free accelerated measurement method is designed and provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 A perspective view showing the pin-on-disc test specified by ASTM;

[0059] Figure 2 A perspective view showing a rock wear test using a solid rock specimen;

[0060] Figure 3 A schematic diagram showing the definition of the spiral radius (r) and the rotation angle (θ) in the Archimedean spiral;

[0061] Figure 4 A graph showing the trajectory of a cutting tool moving along an Archimedean spiral from the center to the outer periphery of a solid rock specimen (called an outward spiral);

[0062] Figure 5 is a graph showing the trajectory of a cutting tool moving along an Archimedean spiral from the outer periphery to the center of a solid rock specimen (called an inward spiral);

[0063] Figure 6 A cross-sectional view showing the adjustment of the cutting depth when a solid rock specimen forms an inward spiral trajectory;

[0064] Figure 7 A schematic diagram showing interference (collision) between the central portion of a rock specimen and a tool holder as cutting is performed in a cutting test on a solid rock specimen;

[0065] Figure 8 Schematic diagrams of an inward spiral (left side), an outward spiral (center), and an inward and outward spiral (right side) according to a first embodiment of the present invention;

[0066] Fig. 9 is a perspective view showing an example of a hollow specimen used in the second embodiment of the present invention;

[0067] Fig.10 To show the spacing distance (R offset ) is a schematic diagram of the inward spiral path (left side) and the outward spiral path (right side);

[0068] Fig.11 Schematic diagrams showing an inward spiral (a), an outward spiral (b), and a slope discontinuity (c) at a position where the inward spiral is connected to the outward spiral formed on a hollow test piece;

[0069] Fig.12 A graph showing the region of s and R where the difference in the slopes of the two helices at the junction of the inward helix and the outward helix is ​​less than 1°;

[0070] Fig.13 It is a schematic diagram of the cutting knife and cutting track provided on the cutting head;

[0071] Fig.14(a) and (b) are schematic diagrams showing the length of the outer contour line (Lc) of the cutting head and the interval (s) between the cutting knives;

[0072] Fig.15 A schematic diagram showing the penetration depth during the feed operation;

[0073] Fig.16 A schematic diagram showing the operating speed and the pressing depth during the shearing operation;

[0074] Fig.17 is a graph showing the ratio (Rt) of the contact time corresponding to the cutting depth (y) during shearing operation;

[0075] Fig.18 is a graph showing the relationship between cutting depth (d) and cutting load (Fc);

[0076] Fig.19 It is a graph showing the changing trend of cutting load (Fc) and vertical load (Fn) corresponding to uniaxial compressive strength (UCS). DETAILED DESCRIPTION

[0077] [First embodiment]

[0078] In the first embodiment, the cutting tool moves inward and outward alternately and repeatedly, and the cutting tool cuts the rock specimen in the process of moving along different Archimedean spirals when moving inward and outward. The end point of the inward movement becomes the starting point of the outward movement, and the end point of the outward movement becomes the starting point of the inward movement. The rotation direction of the rock specimen is the same when moving outward and inward.

[0079] According to this method, the rock specimen continues to rotate in the same direction, so there is no burden on the specimen rotating motor. In contrast, when the rotation direction of the rock specimen changes instantly in the opposite direction at the end of the inward spiral and the end of the outward spiral, a burden is placed on the motor, etc.

[0080] Figure 8 The spiral trajectory of the cutting tool when it moves inward (left figure, inw), the spiral trajectory when it moves outward (middle figure, outw) and the overlap of the inward spiral trajectory and the outward spiral trajectory (right figure) in the first embodiment are respectively shown.

[0081] The inward spiral starts from (R, 0) on the x-axis and moves inward (inward spiral, inw) → outward (outward spiral, outw) → inward (inward spiral) → outward (outward spiral)... The cutting is repeated alternately, moving along different trajectories (paths) and the rotation direction of the rock specimen is the same.

[0082] The trajectory of the inward spiral is shown in equations (A) to (E). [t=0~(Tt0 )].

[0083]

[0084] r inw =Rf inw (t)...................(B)

[0085] θ inw =2πNf inw (t)-θ f ...................(C)

[0086] P xinw =r inw ·cos(θ inw )...................(D)

[0087] P yinw =r inw ·sin(θ inw )...................(E)

[0088] The trajectory of the outward spiral is shown in equations (F) to (J). (t = t 0 ~T).

[0089]

[0090] r outw =Rf outw (t)...............(G)

[0091] θ outw =-(2πNf outw (t)-θ 0 )+(θ 0 -θ f )...................(H)

[0092] P xoutw =r outw ·cos(θ outw )...............(I)

[0093] P youtw =r outw ·sin(θ outw )...............(J)

[0094] In the above formula, r is the radius of the cutting tool, R is the radius of the test piece, and R 0is the radius of the starting position of cutting when moving outward or the radius of the ending position of cutting when moving inward, and s is the interval between spirals (see Figure 3 ), v is the moving speed of the cutting tool moving along the spiral. The parameters in the above formula can be calculated by formula (K). In addition, inw represents inward movement, and outw represents outward movement.

[0095]

[0096] θ 0 is to make the radius (R 0 ) and angle are consistent with the starting radius and angle of the outward spiral, θ f This is a value that is applied to start a spiral inward from (R, 0) on the x-axis (the phase angle at the time point when the previous spiral ended).

[0097] The calculation is performed by setting constants as shown in the following table. Figure 8 (Although the trajectories (paths) of the two spirals are different, the function constant is the same.) The outward spiral begins where the inward spiral ends, so the different spiral paths move in the same rotational direction.

[0098] [Table] Examples of constants used in the Archimedean screw wear test of rock specimens

[0099] R[mm] <![CDATA[R 0 [mm]]]> s[mm] v[mm / s] 200 40 20 10

[0100] like Figure 8 As shown in the right graph of , the instantaneous slope (dy / dx) of the spiral path when switching from the inward spiral to the outward spiral is different (about -1.71 for the inward spiral and about -1.12 for the outward spiral), so the connection between the spirals is not smooth. (See Figure 8 In particular, this slope difference increases with the spiral spacing (s) because different spirals with the same radius have different slopes.

[0101] The slope difference can be calculated by the following formula.

[0102] Δθ=|(dy / dx) inw -(dy / dx) outw |

[0103] By adjusting the four constant values ​​in the above table, it is preferred that the slope difference between the end point of the inward movement and the start point of the outward movement and the slope difference between the end point of the outward movement and the start point of the inward movement be 0.5° to 5°, and more preferably less than 1°. If the slope difference is greater than 5°, the connection between the spirals is not smooth, which may cause problems in continuous data acquisition. If the slope difference is less than 0.5°, the intervals between the spirals are too close, so there may be problems in the test, which is not preferred.

[0104] As mentioned above, in the case of different paths and the same rotation direction, the paths of the inward spiral and the outward spiral are different, so it is difficult to calculate the spiral. In particular, with the inward spiral / outward spiral conversion, the end position and angle need to be used as the initial starting position and angle input to realize the path so that the end time point of the spiral path is consistent with the start time point. To this end, the angle needs to be calculated as follows (Formula C, Formula H).

[0105] When moving inward for the first time: θ 1 (t)=2πNf inw (t)-θ f

[0106] When moving outward for the first time: θ 2 (t) = -(2πNf outw (t)-θ 0 )+θ 1 (Tt 0 )

[0107] When moving inwards for the second time: θ 3 (t)=2πNf inw (t)+θ 2 (T)

[0108] When moving outward for the second time: θ 4 (t) = -(2πNf outw (t)-θ 0 )+θ 3 (Tt 0 )

[0109] When moving inward for the hth time (h ≥ 3): θ 2h-1 (t)=2πNf inw (t)+θ 2h-2 (T)..............(L)

[0110] When moving outward for the hth time (h ≥ 3): θ 2h (t) = -(2πNf outw (t)-θ 0 )+θ 2h-1 (Tt 0).....(M)

[0111] In the above formula,

[0112] t: time

[0113] N: number of spirals

[0114] f inw (t): satisfies f inw (0) = 1, f inw (1) = 0. For example

[0115] f outw (t): satisfies f outw (0) = 0, f outw Any function where (1) = 1. For example

[0116] T: The time required for the cutting tool to move from the center of the rock specimen to the outer contour or from the outer contour to the center along the spiral trajectory

[0117] Tt 0 : The time the cutting tool moves along the spiral track.

[0118] θ 0 :In order to make the radius at the end point of the inward movement (R 0 ) and angle to match the starting radius and angle of the outward movement.

[0119] According to the above angle calculation method, the formula for calculating the angle shows regularity in the process of moving inward (inward spiral) → moving outward (outward spiral) → moving inward (inward spiral) → moving outward (outward spiral)... In other words, the angle is calculated by reflecting the ending angle of the previous spiral, and the method for calculating the angle of the inward spiral is different from that of the outward spiral. Based on the above formula and regularity, a continuous spiral path with the same rotation direction can be generated.

[0120] [Second embodiment]

[0121] 1. Pin-to-disk for hollow rock specimens

[0122] (1) New intrinsic constant (R offset )

[0123] Fig. 9 1 is a perspective view showing an example of a hollow test piece. As shown in the figure, a hollow (hollow space) is formed in the center of the hollow test piece in the vertical direction.

[0124] During the cutting test, after n wears are completed, the cutting depth needs to be adjusted and n+1 wears need to be performed. The cutting depth can be adjusted vertically by moving the test piece outward or outward to the hollow side by a certain length. At this time, the radial length of the excess is defined as R offset .

[0125] In addition, in the present invention, a motor (not shown) is used to rotate the rock specimen, and it takes time to accelerate the motor, so the set constant speed cannot be met from the beginning of the test. For this reason, it is necessary to set R offset To ensure the acceleration range. Fig. 9 Equivalent to R offset The acceleration time is t 1 -t 0 and Tt 2 The acceleration time needs to be set sufficiently compared to the motor specifications so that the wear test can be performed after reaching a constant speed.

[0126] (2) Arrange variables according to the shape of the test piece

[0127] The variables required for conducting the Archimedean screw test (pin-on-disk test) on hollow rock specimens are summarized as follows.

[0128] R: outer radius of hollow test piece [mm]

[0129] R 0 : Inner radius of hollow test piece [mm]

[0130] R offset : The length of the cutting tool (Pick cutter, etc.) going out of the hollow test piece or the length of the cutting tool moving into the hollow part [mm].

[0131] t 0 :The cutting tool moves from the rotation center of the hollow test piece to (R0-R offset )Time required [s]

[0132] t 1 :The cutting tool moves from the rotation center of the hollow test piece to R 0 Time required [s]

[0133] t 2 : The time required for the cutting tool to move from the rotation center of the hollow test piece to R [s]

[0134] T=T total :The cutting tool moves from the rotation center of the hollow test piece to (R+R offset )Time required [s]

[0135] T move: The time taken by the cutting tool to actually move during the cutting test. That is, from (R 0 -R offset ) moves to (R+R offset )Time taken [s]

[0136] T test : Actual wear test time of hollow rock specimen (contact time with specimen, t 2 -t1)[s]

[0137] N(=N total ): Mathematically from the center of the test piece to (R+R offset ) Total number of spirals generated

[0138] N move : The number of spirals actually achieved in the cutting test

[0139] N test : The number of spirals formed in the area where the cutting tool contacts the hollow rock specimen

[0140] s: spacing between spirals [mm]

[0141] v: The speed of the cutting tool moving along the spiral [mm / s].

[0142] In this experiment, five intrinsic constants defining the Archimedean screw test are shown below, and the remaining test variables are dependent constants calculated from the intrinsic constants.

[0143] Table 1: Five inherent constants of the Archimedean spiral wear test on hollow specimens

[0144] R[mm] <![CDATA[R 0 [mm]]]> <![CDATA[R offset [mm]]]> s[mm] v[mm / s]

[0145] (3) Arrangement of the intrinsic constant relationship

[0146] The relationship between the dependent constant and the intrinsic constant is calculated by the following formula. Total number of spirals (N = N total ) and the actual number of spirals moved (N move ), the number of spirals formed by the actual contact with the test piece (N test ) can be calculated as follows.

[0147]

[0148] The relationship with respect to the movement time variable can be calculated as follows.

[0149]

[0150] That is, T = T total′ T move =Tt0 T real =t 2 -t 1 .

[0151] The travel distance variable can be calculated as follows.

[0152]

[0153] Among them, L inwtotal , L inwtest , L outwtotal , L outwtest They represent the total moving distance in the inward direction, the cutting test distance in the inward direction, the total moving distance in the outward direction, and the cutting test distance in the outward direction, respectively.

[0154] And, the trajectory of the inward spiral (P xinw , P yinw ), the outward spiral trajectory (P xoutw , P youtw ) is as follows.

[0155] P xinw =r inw ·cos(θ inw )..................(12)

[0156] P yinw =r inw ·sin(θ inw )...................(13)

[0157] P xoutw =r outw ·cos(θ outw )...................(14)

[0158] P youtw =r outw ·sin(θ outw )...................(15)

[0159] In the above formula, P xinw , P yinw : The position coordinates of the cutting tool at a specific time (t) when moving inward

[0160] r inw : The radius of the cutting tool position at a specific time (t) when moving inward

[0161] θ inw : Phase angle of the cutting tool position at a specific time (t) when moving inward

[0162] P xoutw , P youtw : The position coordinates of the cutting tool at a specific time (t) when moving outward

[0163] r outw : The radius of the cutting tool position at a specific time (t) when moving outward

[0164] θ outw : Phase angle of the cutting tool position at a specific time (t) when moving outward

[0165] The rotary motor that rotates the rock specimen and the linear motor that moves the cutting tool are all controlled by speed. Therefore, the path equation (Equation 12 to 15) represents the current position of the cutting tool, so it is necessary to differentiate it and convert it into linear speed and RPM.

[0166] Consider R offset In the case of radial velocity (v routw , v rinw ) and RPM(RPM outw , RPM inw ) is shown in the following formula.

[0167]

[0168] In the above formula, V routw : When moving outward, the radial linear moving speed of the cutting tool

[0169] RPM outw : The rotation speed of the rock specimen when moving outward

[0170] V rinw : When moving inward, the radial linear moving speed of the cutting tool

[0171] RPM inw : The rotation speed of the rock specimen when moving inward

[0172] (4) Example of spiral test design

[0173] The simulated moving paths of the five inherent constant values ​​of the spiral wear test are arbitrarily specified as shown in Table 2. The calculation output table of the spiral function corresponding to the five constants is shown in Table 3.

[0174] [Table 2] Five inherent constants of the Archimedean screw wear test for hollow specimens

[0175]

[0176] [Table 3] Example of test variable output value arrangement

[0177]

[0178] In addition, the trajectory of the inward spiral (Re) is shown in a graph as Fig.10 As shown in the left curve graph, the trajectory of the outward spiral (Bl) is shown in the curve graph as Fig.10 As shown in the right curve graph. Fig.10 In the figure, the gray path (gr) represents the overall path, and the red (Re) and blue (Bl) paths represent the actual cutting paths.

[0179] (5) Solve the problem of spiral discontinuity

[0180] Fig.11 The paths (a) of an inward spiral, (b) of an outward spiral, and (c) of a case where the path moves inward and then outward are shown. Fig.11 The direction of rotation of the rock specimen is the same when moving inward and outward. When the test is carried out continuously as above, a discontinuity in the slope of the spiral occurs at the time of changing from the inward type to the outward type. If the discontinuity angle increases excessively, the equipment may be overloaded, so these need to be considered when designing the test.

[0181] From experience, the applicant has found that when the slope difference between the end point of the inward movement and the start point of the outward movement and the slope difference between the end point of the outward movement and the start point of the inward movement is less than a specific angle (δ°), the direction change during the wear test can become gentle, and the applicant has found that the preferred specific angle is 1°. This is shown in Formula 20 when expressed in a numerical formula. If the slope difference is more than 1°, the connection between the spirals is not gentle, so the motor movement is extremely variable, so problems such as excessive equipment burden may occur, so it is not preferred.

[0182]

[0183] Therefore, the area where the angle is kept less than 1° is investigated, and the range of the specimen radius (R) and the spiral spacing (s) at this time is as follows: Fig.12 Simulation was performed. It was found that the area less than 1° and the area greater than 1° are almost linearly separated. The inequality at this time is shown in equation 21. Therefore, when the specific angle is set to 1°, it is safer to set the test variable within the range of this equation. The range of the following inequality is an example.

[0184] s<0.033R-5.334(where, D grad <1°)...................(21)

[0185] 2. Accelerated life wear test design

[0186] (1) Cutting condition calculation method

[0187] like Figures 13-14 As shown, the picks (an example of a cutting tool) of the cutting head have different rotational tracks. Therefore, the designed cutting interval (s) can be estimated by dividing the total length of the track by the number of picks arranged on the cutting head. That is, the cutting interval (s) is calculated by dividing the length of the contour line (Lc) at the end of the roller of the cutting head by the number of picks (n). For reference, Fig.14 In the box, '+' and 'x' represent cones.

[0188] s=L c / n...................(22)

[0189] The penetration depth indicates the depth of the rock cut by the cutting head for each rotation. The cutting operation of the cutting head can be divided into the feeding operation and the shearing operation.

[0190] The depth of penetration during the cutting operation (d sump ) is generally described in the equipment's operating manual. Fig.15 The x value (X1, X2, etc.) is the depth of penetration per revolution (d sump ).

[0191] The penetration depth per turn during shearing operation (d shear )like Fig.16 As shown in the figure, according to the lateral movement speed of the cutting head (slewing or shearing speed: v shear ) and the rotation speed (rpm). shear The formula is as follows.

[0192]

[0193] (2) Cutting speed conversion

[0194] The cutting speed is determined by converting the designed rotational speed (rpm) or linear speed (vl) value of the cutting head. This uses the conversion formula of linear speed from the cutting head to the end of the cone and rotational speed, which is equation 24. In most cases, the radius of the drum can be set to r. The cones at the ends of the two sides of the cutting drum, i.e. the nose, are located at different positions on the radius of the drum, so it is necessary to consider the position of the corresponding cone and set the r value.

[0195]

[0196] (3) Cutting distance conversion

[0197] The cutting head continues to contact the bedrock while the equipment is working, however, the cone only contacts the bedrock part of the time. Therefore, the cutting time of the cone changes with the contact angle with the contact surface during operation. The operation is divided into feeding and shearing.

[0198] ① Cutting distance during feed operation

[0199] Think of the interval when half of the cutting head is pressed in from the start of the feed. The initial contact time of the drum type boring machine is 0, and the maximum feed depth is pressed to the radius of the drum (D / 2 = R). Therefore, the ratio of contact time to working time (Rt = ratio of contact time) is 50%, so it can be assumed that the average contact cutting time is 1 / 4 times. Therefore, the cutting distance (Lc) of each cone can be calculated using the boring machine working time (t) as follows.

[0200]

[0201] ②Cutting distance during shearing operation

[0202] Except for the first shearing operation section, the tunnel boring machine is operated while keeping the vertical excavation depth (y) value below 1 / 2 to 1 / 4 of the drum diameter (D). This is because it can speed up the excavation speed. The results of the investigation on the working depth ratio (y / D) and contact time ratio (Rt) of the cutting drum during shearing operation are as follows Fig.17 As shown. The linear regression is obtained as the following formula 26, so the shearing time (t) of the entire cutting distance is calculated as formula 27. (where R t The maximum value is 0.5)

[0203] R t =0.36+0.15(y / D)(where, R t ≤0.5)...................(26)

[0204]

[0205] (4) Cutting load accelerated life test method

[0206] ①Method for adjusting cutting depth (d)

[0207] It is known that the cutting load (Fc) increases linearly with increasing cutting depth in the same rock. Therefore, an accelerated life test can be designed by adjusting the cutting depth (cutting depth, d) to increase the cutting load. When d = 0, the cutting load is also 0, so it is more reasonable to assume that the y-intercept of the linear regression equation is 0. Therefore, the cutting load corresponding to the penetration depth can be predicted by the following linear function. Among them, a is the slope of the linear function, which is a coefficient calculated by experiment.

[0208] F C =ad...................(28)

[0209] The tunnel boring machine can dig to the initial area of ​​hard rock. Therefore, the data was analyzed by setting the weakest soft rock as 10MPa based on the compression strength standard and the initial area of ​​hard rock as 100MPa. The minimum-maximum range of the slope is 3 to 11. Fig.18 shown.

[0210] ②Methods for comprehensive adjustment of rock properties and cutting depth

[0211] There is a method to improve the accelerated life by improving the physical properties of the rock to be cut. Generally, the uniaxial compressive strength (UCS) of rock has a typical physical property trend, so accelerated life wear tests can be performed by increasing UCS. Among them, when UCS and d are selected as input variables and the cutting load (Fc) is selected as the output, their relationship can be regressed into a specific function. A typical example of this regression equation is shown below. Among them, Fc = cutting load, UCS = uniaxial compressive strength, d = cutting depth, a, b and m, n are the coefficients of the regression equation respectively.

[0212] F C =[a UCS+b]d............(29)

[0213] F C =[m UCS (n) ]d...................(30)

[0214] The power function of equation 30 is more accurate, but for convenience, the linear function shown in equation 29 is also used extensively. The coefficient values ​​of a and b in the equation can be determined to complete the model of increased cutting load. Accelerated life tests can be designed based on this. According to the experimental results of existing research (Bilgin, 2006), the range from soft rock to hard rock has values ​​of a=0.83, b=21.8, m=2.3, and n=0.8 (N. Bilgin et al., Dominant rock properties affecting the performance of conical picks and the comparison of some experimental and theoretical results International Journal of Rock Mechanics & Mining Sciences 43 (2006) 139.156).

[0215] The vertical load during cutting can also be estimated using the following formula 31. It has been reported that in the case of vertical load, it can be estimated by n = 1. Therefore, it can be expressed by the following linear formula with a coefficient of 1 (see Fig.19 ). That is, as the bedrock strength increases, the vertical load increases more than the cutting load, so it is known that care must be taken when cutting hard rock or heavier rock.

[0216] F N =[m UCS (n) ]d=[m UCS]d............(31)

[0217] ③Cutting speed acceleration test

[0218] You can also increase the cutting speed to perform an accelerated life test. For cutting speed, just increase the tool's additive moving speed (vRe, resultant velocity). It is as follows.

[0219]

[0220] In the above formula, v r Indicates the radial linear velocity of the cutting tool, v t Indicates the tangential rotation speed of the tool. As a result, the added moving speed is the final speed, so it is necessary to convert this speed in order to design the acceleration test.

[0221] (5) Setting the acceleration factor for accelerated life test

[0222] ① Load of accelerated life test

[0223] (i) Equivalent load

[0224] The evaluation value of the cutting load (Fc) described above can be defined as an equivalent load. The average value of the cutting load cannot be extracted through actual vehicle testing, so it is necessary to derive the average value based on the data obtained through linear cutting tests or rotary cutting tests. Suppose the real-time test load extracted from the cutting test is Fc(t), the number of samples: n, t1: start time (sec), t 2 :End time (sec), f s :The equivalent load formula for sampling frequency (sampling frequency, Hz) is as follows.

[0225]

[0226] where n = f s (t 2 -t 1 )

[0227] (ii) Acceleration load

[0228] Acceleration load (Fc a ) is the value determined during the test design, the acceleration load ratio (a F ) is calculated by the following formula 34. Wherein, λ is the fatigue damage index, which is a value that defines the degree of damage to each component corresponding to the load, and is calculated by regression of the SN curve obtained by fatigue testing or fatigue analysis. Generally, a value of 2.0 is used for bearings and gear parts.

[0229]

[0230] ②Speed ​​of accelerated life test

[0231] (i) Equivalent speed

[0232] The equivalent speed represents the average resultant speed of the working force. As described above, it is calculated using the rotation radius of the equipment and rpm, as shown in Equation 35.

[0233]

[0234] (ii) Acceleration speed

[0235] The ratio of acceleration speed during the test (a v ) with acceleration speed (v a ) and equivalent speed (v eq ) is expressed as follows. v) is the fatigue damage index with respect to speed. For rock cutting tools where the effect of wear caused by speed difference is unknown, it is assumed to be 1.0.

[0236] Acceleration speed (v a ) is one of the five intrinsic constants and is set by the experimenter. For example, the equivalent speed of the tunnel boring machine (v eq ) is 1.5m / s, the user sets the acceleration speed to 30(v a ) is 3.0m / s, and when the fatigue damage index is 1.0, the acceleration speed ratio is 2.0. At this time, for the acceleration speed, the radial speed and the tangential speed should be accurately controlled according to the above formula.

[0237]

[0238] ③Acceleration factor

[0239] By multiplying a F with a v The acceleration factor (AF) is calculated. When this acceleration factor is set, the test time and excavation amount of the accelerated life test can be greatly reduced.

[0240] AF=a F a v ...................(37)

[0241] ④ Fault-free excavation volume calculation formula

[0242] It is known that the failure-free test time is defined as the minimum time that a product should work without failure in the actual use environment in order to meet the reliability target. That is, the Rx(%) of the product is C(%) trusted to work without failure until Lx time, and no failure should occur during the failure-free test time in the actual use environment. And the method for calculating the failure-free test time is well known.

[0243] However, for rock cutting tools, it is more reasonable to set the excavation volume as the test target rather than the test time. This is because the equipment operation rate is usually less than 50%, especially according to its operation scene, the contact time of each rock cutting tool (e.g., cone) varies greatly, so in many cases it is impossible to accurately estimate the rock cutting tool operation time.

[0244] Therefore, it is preferable to use the reliable excavation volume (Lv) instead of the product reliable life (Lx). In this case, the volume used to calculate the trouble-free excavation volume and the trouble-free accelerated excavation volume (Vc a ) is shown below.

[0245]

[0246] In the above formula, L v :Reliable excavation volume (=Reliable life, m 3 ), V c :Fault-free excavation volume (m 3 ),

[0247] AF: acceleration factor, C: reliability level, n: number of samples, R x : reliability,

[0248] β: Fault characteristic index (shape parameter),

[0249] C, n, and Rx are dimensionless constants, so the units of the entire formula are unified as volume units.

[0250] Among them, the excavation failure-free accelerated excavation volume (Vc a ) period, assuming that no failure occurs when the product is tested with an accelerated load cycle, then Rx(%) for a specific tool product indicates that it can be trusted that failure will not occur when digging to the Lv cutting volume position.

Claims

1. A method for measuring wear and evaluating durability of a rock cutting tool, characterized in that: When the rock specimen is rotated with the center of the rock specimen as the reference, the cutting tool repeatedly moves linearly from the outer contour of the upper surface of the rock specimen to the center, cutting the rock specimen inward, and moving linearly from the center to the outer contour, cutting the rock specimen outward. The cutting tool forms a spiral trajectory at a certain speed when moving inward and outward, and the interval between the spirals is certain. The rock test piece is a test piece with a hollow formed vertically in the central part. When the cutting tool moves inward, it moves toward the hollow at least a predetermined distance to adjust the pressing depth and then starts to move outward. When moving outward, it moves outward to the outside of the rock test piece for a certain distance to adjust the pressing depth and then starts to move inward. The wear measurement and durability evaluation method is realized by an accelerated life test, by increasing the cutting load Fc and the cutting speed v Re At least one of them is implemented; In the accelerated life test, the reliable excavation volume L v Replace the concept of reliable time to define reliable life. The trouble-free accelerated excavation volume Vc is calculated by the following formula: a , [Mode] In the above formula, Vc: Fault-free excavation volume, m 3 , L v : Reliable excavation volume, i.e., reliable life, m 3 , C: reliability level, n: number of samples, Rx: reliability, β: Fault characteristic index, i.e. shape parameter, AF: acceleration factor.

2. The wear measurement and durability evaluation method of a rock cutting tool according to claim 1, characterized in that: When moving inward, the cutting tool is separated from the outer side of the rock specimen by a distance of R. offset The position of the spiral moves into the rock specimen, When the cutting tool moves outward, it is separated from the center of the rock specimen by a distance R o -R offset The position of the spiral moves into the rock specimen. R o is the radius of the hollow.

3. The wear measurement and durability evaluation method of a rock cutting tool according to claim 1, characterized in that: The AF is calculated by the following formula: [Mode] AF=a F a v In the above formula, aF: acceleration load ratio, Fc a , i.e. acceleration load: the value determined during the test design, Fc eq , that is, equivalent load: the average value of cutting load Fc within a certain time t1~t2, Where n = f s (t2-t1) f s : sampling frequency, Hz, Fc(t): Real-time cutting load λ, fatigue damage index: is a value that defines the degree of damage to each component relative to the load. a v : The ratio of acceleration speed, v a : acceleration speed, v eq : Equivalent speed, r: the radius where the cutting tool is located, rpm: rotation speed of the rock specimen, λ v : Fatigue damage index with respect to speed.

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